The lineset is the original lineset. It is secure in the attic, but who knows if it secure in the wall. I would think yes, because I cannot move it much in the vertical section, when messing with it in the attic. The lineset set is perfect. I think it is 5/8 and 3/8, which is what the xl15i was spec'd for. I called trane and if necessary, there seems to be a way to get a field rep. I am hoping I won't need it. The problem is the noise is not horrible. But, it is damn annoying and should not be, or they wouldn't sell too many of these things. I am thinking maybe they can move the unit a foot further away from the wall and my unit and put it on isolators.

Thanks, klem1. I raised my concerns regarding noise with the sales guy when he came out to make a proposal and then with the installer the day it was going to be installed. Each time I was assured that this unit would be much quieter than my old one. Within a couple of days of installation in November, I contacted the installer to complain. After doing some exploration, they proposed ordering a Trane soundblanket and said that it should make a difference. The soundblanket took almost two months to get installed (late December), and didn't make a discernible difference. After I complained that the soundblanket didn't help, they came out last week. During that visit, they said that since the unit appears to comply with Trane's reported noise ratings on Trane's website - although with my son's window open, it pretty much hits the reported 74dbs using an iphone app (it's actually louder above the unit than next to it) - they can't replace it under warranty etc. and they can't resell it as new equipment so there's not much they can do. They have offered to move the unit to my driveway, but that is about 25' from its current location, would take up a fair amount of space in the driveway, and runs the risk of theft etc. unless I build a fence around it. Any ideas of how to convince the installers to try another unit? Thanks so much in advance.

Our Carrier heat pump is now 10 years old. The outdoor unit was very quiet when first installed, but weather and age lead to rattles. I cut thin strips of rubber to act as bushings/washers to silence the rattles between metal/metal or plastic/metal connections (grill/body panels). Our Silencer system is now silent again. We replaced the indoor air handler at the same time as the outdoor unit. I specifically wanted a quiet fan because our old one was loud. The A/C guy sold me on the single stage, variable speed unit and he also installed a sound deadening baffle where the air handler connects to the old metal duct work. In addition, the unit sits on rubber bushings on the concrete floor. It works well, especially the way it slowly ramps up to speed, and is generally quiet. The only time it will make a loud noise is in the winter if you set your thermostat really low at night and then the metal ducts will pop in the early morning due to the higher thermostat setting coming on. We solved this problem by only dropping the temp 2 degrees at night for better sleeping/economy. Heat pumps tend to work best with small changes in demanded temperature. We also have the electric strip backup, but it rarely comes on. It's been a great system, and I hope it lasts 20 years.

Defrost, yes. During defrost the unit switches back to cooling mode so the outside coil gets warm to melt any accumulated frost. The outside fan usually shuts off to retain the heat in the coils while the compressor runs for defrosting. The indoor blower runs and the auxiliary heat strips activate to counteract the cold air that otherwise would be blowing inside. The refrigerator reversing valve changes back to heating mode at end of the defrost cycle, which is the source of the pressure release sound.